This invention relates generally to ion source methods and apparatus, and, more particularly, relates to apparatus and methods for providing enhanced liquid metal ion source life and beam current stability.
Liquid metal ion sources have been employed in a variety of electrostatic optical systems in recent years. Such systems are utilized in a variety of applications, including ion beam lithography and direct ion implantation in such fields as semiconductor processing, ion mass spectrometry, and sub-micron machining.
In many ion beam-based processes, such as photomask and circuit repair, and maskless ion implantation, ion beam current and impingement position must be carefully controlled, requiring highly stable ion beam currents. A typical liquid metal ion column includes an ion source, which generates ions from a selected liquid metal, and one or more downstream electrodes to generate and focus an ion beam from the ions provided by the ion source. The ion beam impinges on a work piece to perform the required application.
Ion beam instabilities often result, however, from the liquid metal ion source itself. A conventional gallium liquid metal ion source, for example, includes a tungsten filament wetted by a gallium film. In this configuration, ion emission is a function of the constant supply of gallium to the filament tip, which sustains the characteristic "Taylor cone." This source flow propagates through a thin film, which, if interrupted or reduced in thickness, can destabilize ion beam current and reduce ion source life.
Degradation of source flow can result from "backsputtering," a process in which ions from the ion source strike downstream elements, sputtering off particles that, in turn, strike the ion source. These backsputtered particles can adversely affect liquid metal ion source performance, including source life and short- and long-term ion beam current stability.
It is thus an object of the invention to provide ion source methods and apparatus affording enhanced source life.
If is another object of the invention to provide such ion source methods and apparatus which afford improved short- and long-term ion beam current stability.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.